1. Field of the Invention
The present invention relates to a rotary laser beam emitter which rotates to irradiate a laser beam in a level plane.
2. Description of the Related Art
In surveying work for civil engineering, it is well known that a height and an inclination angle of a target relative to a level plane is measured using a rotary laser beam emitter which is placed on a known point and rotates to irradiate a laser beam in a level plane. The laser beam from the rotary laser beam emitter is received by a light receiver to measure an incidence angle and a height relative to a level plane orthogonal to a rotary axis of the rotary laser beam emitter at the light receiving position. Such a rotary laser beam emitter comprises a beam emitting unit rotatable on a base unit to emit a laser beam in a direction orthogonal to the rotary axis. To improve an accuracy of measuring the inclination angle and height, the rotary laser beam emitter is required to reduce a variation in an exit angle of the laser beam relative to the rotary axis as much as possible.
Japanese Laid-open Patent Publication No. 2006-71545 discloses a rotary laser beam emitter which comprises a rotary element rotatable around a rotary axis on a base unit and accommodating a plurality of pentaprisms longitudinally arranged on the rotary axis, and a light source on a base unit which emits a laser bean towards the pentaprisms in a rotary axis direction, for example. In this rotary laser beam emitter, by rotation of the rotary element relative to the base unit, each pentaprism is rotated to reflect and change the exit direction of the laser beam from the light source. The pentaprisms (rotary element) can be stably rotated since they are longitudinally arranged inside the rotary element on the rotary axis, which can substantially reduce a variation in the exit direction of the laser beam due to rotary vibrations or else.
However, a problem arises in this rotary laser beam emitter when another measuring device (GPS receiver, for example) is mounted above the pentaprisms (on the rotary element) that the measuring device is rotated together with the rotary element. In order to prevent this, it is possible to provide an outer case for the rotary element to be able to rotate inside the case and a plane to mount the measuring device above the case. However, the case needs to include a vertical connecting portion to the base unit outside the rotary element, and there still remains a problem that the connecting portion interrupts the emitted laser beam in a part of the rotary direction of the rotary element.
Instead of the outer case, a shaft element can be provided on the base unit to be coaxial with the rotary axis and extend from the base unit along the rotary axis. It can be configured to insert the shaft element into a through hole of the rotary element. Thereby, another measuring device can be mounted over the shaft element.
However, with such a configuration, a light source has to be placed around the rotary axis (that is, shaft element) so that the center of gravity of the rotary element balances off from the rotary axis. This may result in changing a posture of the rotary element relative to the rotary axis and varying the direction of the emitted laser beam, which decreases a measuring accuracy of the inclination angle and height of a target.